Water may become intermixed with diesel fuel or other fuels in several ways, including purposeful mixing, condensation of humid air, during transportation from refineries or other stations to end-distribution holding tanks, by leakage through faulty valves, pipes, or vents, and by careless handling. Water can cause injector nozzle and pump corrosion, microorganism growth, and fuel filter plugging with materials resulting from corrosion or microbial growth. In cold climates, ice formation in fuels containing water may cause fuel line and filter plugging problems. Regularly removing any water from the fuel being used is the most effective means of preventing these problems.
Fuel-water admixtures may even be more problematic in a locomotive context. In particular, locomotive engines consume much more fuel than other mobile applications, so there is a potential to accumulate a lot of water. However, for cost and other practical purposes, locomotives generally have only two scheduled maintenances a year. Because of this, locomotives may require large dedicated water holding tanks. Additionally, manually operated purge valves, such as found on some on-highway vehicles, are not practical; that is, a manual water drain strategy does not work well on a locomotive application since railroad practices typically only allow manual intervention every 180 days. Further, locomotive engines run mostly unmanned (operator cannot see the engine), so failures in an automatic drain system that could cause fuel spills must be avoided.